A. Field of the Invention
The present invention generally relates to surge arresters and, more particularly, relates to valve type surge arresters suitable for mounting within the housings of small electrical equipment.
B. Description of the Prior Art
Valve type surge arresters are well known in the prior art and provide protection for associated electrical equipment from overvoltage surges. Examples of prior art surge arresters are disclosed in the following U.S. Pat. Nos: 3,141,108; 3,154,718; 3,435,290; 3,569,786; 3,723,819; and 3,849,704.
A particular need has developed for protecting submerged pump motors and other small electrical equipment from overvoltage surges. The devices disclosed in the U.S. Pat. Nos. 3,435,290 and 3,849,704 patents provide overvoltage surge protection for submerged pump motors. The device of the U.S. Pat. No. 3,435,290 is encased outside of and adjacent to a submerged pump. The device of the U.S. Pat. No. 3,849,704 is disposed inside a pump motor housing. The device of the U.S. Pat. No. 3,849,704 is a small, sealed, expulsion type arrester and has been found to function satisfactorily for shunting ten overvoltage surges including the associated power follow currents to ground. The principal disadvantage of the small, sealed, expulsion arrester is the high internal pressures that are built up within the arrester due to the high power follow currents. In addition, this particular small, sealed prior art arrester requires a minimum well depth of from 30 to 50 feet since it uses the resistance of the power line leads to limit the magnitude of power follow currents.
Thus, a need exists for an improved valve type arrester especially suited for use in providing overvoltage surge protection for submerged pump motors and other small electrical equipment, and preferably of a very small configuration such that the arrester may be mounted within the equipment.